From 99df54f19696e26bea8d6a052d8d91ddb1e4ea65 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Martin=20Mo=CC=88hrmann?= Date: Tue, 6 Sep 2016 13:42:49 +0200 Subject: [PATCH] bytes: encode size of rune read by ReadRune into lastRead to speed up UnreadRune MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit In ReadRune store the size of the rune that was read into lastRead to avoid the need to call DecodeRuneLast in UnreadRune. fmt: name old time/op new time/op delta ScanInts-4 481µs ± 4% 458µs ± 3% -4.64% (p=0.000 n=20+20) Change-Id: I500848e663a975f426402a4b3d27a541e5cac06c Reviewed-on: https://go-review.googlesource.com/28817 Reviewed-by: Russ Cox Run-TryBot: Russ Cox Run-TryBot: Martin Möhrmann TryBot-Result: Gobot Gobot --- src/bytes/buffer.go | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) diff --git a/src/bytes/buffer.go b/src/bytes/buffer.go index fa4a51c17f..2ee3d738ef 100644 --- a/src/bytes/buffer.go +++ b/src/bytes/buffer.go @@ -22,14 +22,18 @@ type Buffer struct { } // The readOp constants describe the last action performed on -// the buffer, so that UnreadRune and UnreadByte can -// check for invalid usage. +// the buffer, so that UnreadRune and UnreadByte can check for +// invalid usage. opReadRuneX constants are choosen such that +// converted to int they correspond to the rune size that was read. type readOp int const ( - opInvalid readOp = iota // Non-read operation. - opReadRune // Read rune. - opRead // Any other read operation. + opRead readOp = -1 // Any other read operation. + opInvalid = 0 // Non-read operation. + opReadRune1 = 1 // Read rune of size 1. + opReadRune2 = 2 // Read rune of size 2. + opReadRune3 = 3 // Read rune of size 3. + opReadRune4 = 4 // Read rune of size 4. ) // ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer. @@ -319,14 +323,15 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) { b.Truncate(0) return 0, 0, io.EOF } - b.lastRead = opReadRune c := b.buf[b.off] if c < utf8.RuneSelf { b.off++ + b.lastRead = opReadRune1 return rune(c), 1, nil } r, n := utf8.DecodeRune(b.buf[b.off:]) b.off += n + b.lastRead = readOp(n) return r, n, nil } @@ -336,14 +341,13 @@ func (b *Buffer) ReadRune() (r rune, size int, err error) { // it is stricter than UnreadByte, which will unread the last byte // from any read operation.) func (b *Buffer) UnreadRune() error { - if b.lastRead != opReadRune { + if b.lastRead <= opInvalid { return errors.New("bytes.Buffer: UnreadRune: previous operation was not ReadRune") } - b.lastRead = opInvalid - if b.off > 0 { - _, n := utf8.DecodeLastRune(b.buf[0:b.off]) - b.off -= n + if b.off >= int(b.lastRead) { + b.off -= int(b.lastRead) } + b.lastRead = opInvalid return nil } @@ -351,7 +355,7 @@ func (b *Buffer) UnreadRune() error { // read operation. If write has happened since the last read, UnreadByte // returns an error. func (b *Buffer) UnreadByte() error { - if b.lastRead != opReadRune && b.lastRead != opRead { + if b.lastRead == opInvalid { return errors.New("bytes.Buffer: UnreadByte: previous operation was not a read") } b.lastRead = opInvalid -- 2.48.1